Wait for coordinated pipeline packages to complete

Builds on !1345 (merged) to implement gitlab-com/gl-infra/delivery#576 (closed).

In a coordinated auto-deploy pipeline, these two jobs will fetch metadata for their respective packagers, get the latest pipeline in the project for the tag, and wait for it to complete. The job will succeed if the pipeline has completed successfully, or will otherwise fail, halting the coordinated pipeline.

The next phase after this is to add a coordinated:deploy job that depends on both of these jobs, and triggers the deploy, knowing that the packages are ready.